1. Field of the Invention
The invention relates to digital image enhancement process and more particularly to a process for color image characterization, enhancement, and balancing.
2. Description of Related Art
Electronic cameras based upon CCD detector arrays are quite capable of acquiring image data across a wide dynamic range on the order to 2500:1. This range is suitable for handling most illumination variations within scenes and lens aperture changes are usually employed to encompass scene-to-scene illumination variations. Typically though, this dynamic range is lost when the image is digitized or when the much narrower dynamic range of print and display media are encountered. For example, most images are digitized to 8-bits/color band (256 gray levels/color band). Therefore, the images captured and displayed by photographic and electronic cameras suffer from a comparative loss of detail and color in shadowed zones. This is known as the dynamic range problem. One of the abilities of the human visual system is to steadily perceive a scene regardless of the changes in lighting conditions.
Previous patents in this field include U.S. Pat. No. 6,580,835 to Gallagher which improves digital images by performing a normalized tone scale conversion based on a central pixel of the image.
U.S. Pat. No. 5,991,456 to Rahman et al. describes a method for improving a digital image which calculates the image intensity at specified positions and adjusts the image intensity according to a mathematical equation.
U.S. Pat. No. 5,640,469 to Lewins et al. describes a method for improving images obtained from infrared or x-ray systems which do not obtain the image using visible light. The method improves the intensity equalization of the obtained image data.
An object of the present invention is to provide a method for enhancing digital images.
Another object of the present invention is to provide a method for enhancing digital images captured in complex background and lighting environments.
Another object of the present invention is to provide a method for enhancing digital images which models the human visual system using a ratio rule learning algorithm.
Another object of the present invention is to provide a method for enhancing digital images which is a neural network concept and in which the enhancement is done mainly by processing an individual pixel of an image and does not rely heavily on information of neighboring pixels.
Yet another object of the present invention is to provide a method for enhancing digital images in which the recurrent neural network learns based on the degree of similarity between the relative magnitudes of the output of each neuron with respect to that of all the other neurons.
Finally, it is an object of the present invention to accomplish the foregoing objectives in a simple and cost effective manner.